Spatial light modulators (SLM's) such as the Digital Micromirror Device (DMD, U.S. Pat. No. 5,061,049) and the Grating Light Valve (GLV, U.S. Pat. No. 5,311,360) are used for applications such as digital displays, digital printing, and maskless lithography. The DMD and GLV both comprise micromechanically actuated mirror elements. The DMD's modulator elements are hinged, tilt-actuated mirrors. The GLV comprises diffraction reflective gratings in the form of interleaved ribbon mirrors, wherein alternate mirrors are translationally displaced to vary the optical phase shift between adjacent mirrors.
An alternative type of micromechanical SLM, which is based on proximate transmission diffraction gratings, is disclosed in U.S. provisional applications 60/116,074 and 60/124,140 (cited in U.S. Pat. No. 6,498,685). In this system, a fixed grating and a movable grating are positioned in close proximity to each other, and zero-order light transmitted through both gratings is modulated by altering the lateral positional relationship between the gratings. (The disclosed system is designed for extreme ultraviolet radiation, but could be adapted for other wavelengths.) An advantage of this type of system is that the modulator elements could be incorporated in a microlens array, eliminating the need for an external spatial modulator and projection optics. Furthermore, the transmission gratings can be controlled to provide very precise and accurate control of the modulated beam intensity. But it would be desirable to employ a similar operational principle with a reflective device, which would allow the modulator's actuator controls and data paths to be placed behind the reflective elements without interfering with the optical light paths.